Process of desalting petroleum



Feb. 24, 1942. F. E. WELLMAN PROCESS OF DESALTING PETROLEUM Filed March 18, 1958 xuwZulmE ju -Zulu FMIFDO 20 A FuJPDO ulr ozltmw Frank E. We/Iman Patented Feb. 24, 1 942 UNITED ST TE s- ATENT" OF C PROCESS OF DESALTING PETROLEUM Frank E. Wellman,Vllichlta Falls, Tex. Application. March 18, 1938, Serial No. 196,758 11 Claims. ,(Cl. 252 -348) This invention relates to improvements in process and apparatus for removing salt from crude petroleum oil.

When crude petroleum is taken from the ground it contains salt in varying quantities from a few grams per barrel to 450 grams per barrel or more. It is essential that this salt be removed before the oil is subjected to refining processes, to avoid clogging the exchanger and heater tubes of the refinery. Under the conditions encountered in modern refining processes certain salts are hydrolyzed with water condensed from steam used for stripping or other purposes inth'e system and form highly corrosive acids. I

Neutralizing agents are not always commercially successful in combating the corrosive effects of these acids, for various reasons. In some cases the neutralizing agent unites with the acid base to form a solid, semi-solid or powder which deposits in the heat exchanger in amounts sufficient to make them inoperative. The removal of the salt content from the crude oil often is difficult and expensive.

The object of this invention is to remove the salt from crude oil efiiciently, effectively, and inexpensively.

The drawing illustrates diagrammatically (partly in section) an installation of an apparatus for practicing the process, but it is to be understood that modifications may be made, within the scope of the invention as claimed, to fit specific needs and requirements, without departing from the spirit thereof.

It is recognized in the art that the washing of crude oil with water is the most efficient way of removing the salt from crude oil, since the salt goes into solution readily in water. Heretofore, the reduction of this theory to commercial practice has been impractical because of the difficulties encountered. In using small amounts of water, separation of the water and oil is slow and sometimes not complete. In using larger amounts of water in the systems heretofore employed, disposal troubles are encountered and larger equipment is necessary.

In commercial practice it has been found that intimate mixing of comparatively small amounts of waterwith oil, tendsto produce tight emulsions; this is because the water must be finely divided'to contact the oil thoroughll'so as to extract the salt content; It is afact that the provision of relatively greater amounts of water in contacting the oil, tends to prevent the formation of emulsions and thus makes separation easier of accomplishments I It is a fact also that the separation is accelerated and made "sharper by mixing large amounts of water; however, water used in excess,

mixed in the manner commonly used, presents difficulties and additional expense. The present invention involvescontacting incoming crude oil with large amounts of water with less expenditure of water than isnecessary when crude is. I

contacted with a lesser amount of water in the customary manner. l

I am aware that recycling of precipitated water has been practiced in the breaking of emulsions, but the present invention recycles the water for the express purpose of preventing emulsions from forming. The excessive flooding prevents the formation of small microscopic globules of water which are necessary for the forming of emulsions. Furthermore, the purpose, scope and intent of this invention is to contact large amounts of water in the manner set forth, only with clean pipe line oil or fractions thereof. It is a fact well known in the art, that some third materialmust be present to induce the formation of an oil and water emulsion.

The principal novel features of this invention are: the control of the water to oil ratio independently of the amount of water necessary for the operator to introduce from sources outside of the system; and the control of the degree of brine saturation used in recycling contact with the oil.

It is a fact that a brine of considerably greater density than fresh water, is an efficient solvent for the extraction of more salt and that this increased gravity differential ratio of the oil and water is of great advantage in accomplishing separation in the settling tank.

The operation of the process is as follows: The settling tank 3 is filled with water to a predetermined operating level indicated by dotted line 4. Salty crude oil is pumped into the system through a pipe line 5 without additional water, through pipe line sections 6 and l in the direc tion indicated by the arrows. The crude oil passes through the system further until it enters settling tank 3 through a distributor 8, which may be circular, cross, or other desired shape, and the oil then flows upward through the water until thetank is filled with oil and water. The tank is now in condition for operation.

Upon starting the operation of the system,

water is withdrawn from the bottom of the setbefore it entersthe mixer l2,but it may be heated further by a heater 13 in the pipe section 1 to compensate for the radiation of the heat lost through recirculation of water in pipe line 3.

The water and oil mixture enters the lower portion of the settls'ng tank 3 and is preferably dispensed through a perforated distributor 8. which may be' circular, cross or;other desired shape. The water and oil passingout of the distributor 8 pass upward through the water bath in the lower portion of the settling tank 3 which causes the oil to rise upward and the water con.- taining the salt to settle out. A density float I4 is submerged in the lower portion of settling tank 3 and is so balanced that when the water exceeds the desired degree of saturation this float M will operate a valve l5 and will supply fresh water in to thesyst-em through pipe line l6. This in turn reduces the concentration and raises the water level until the excess is discharged to maintain the water level in the tank. As soon as the specific gravity of the fluid is reduced, the operations automatically reverse themselves and conditions become static until the specific gravity of the brine is raised sufficiently to raise the float Id, at which time the cycle is repeated. This operation will be readily understood and may be performed manually by any one skilled in the art. Several points for introduction of fresh water into the system have been provided, as certain crude oils respond more readily to one system than the other. However, one method of introducing fresh water is through a pipe line l1 admitting the fresh water at connection l8 to the incoming salty crude oil of pipe line 5. It is then carried through pipe section 6 and mixer 19 therein where the fresh water and salty crude oil are intimately contacted and intermixed. A check valve 20 may be provided in pipe section 5 to prevent the pressure of the pump III from causing water in pipe line 9 to enter pipe section 6.

Suflicient pressure is maintained on pipe section 6 from the pipe line 5 to force the oil mixture through pipe section 1. The salty oil, or salty oil and fresh water, that is introduced from pipe section 6, through pipe section I, is further contacted and mixed with a larger amount of water that is obtained from the bottom of the settling tank 3 and flows through pipe line 9. The water and salty oil are passed through mixer l2 and into the bottom of the settling tank 3 through the distributor 8. As the water level rises in the tank by the introduction of fresh water, float 2|, which is adjusted to float between the oil and water, will cause a valve 22 to open and dis.- charge the salt saturated water from the bottom of the tank until the water in the settling tank recedes to the desired level.

As long as the water does not become salt saturated beyond the desired degree, no further water will be introduced, and the system will operate on the water contained in the settling tank and in pipe lines I and 9. In this manner much heat tlingtank- 3, is through pipe line 9 by use of the pump iii, with the valve i9 closed and valve 30 open. This will direct the water through pipe line section 9' into connection 3| where it is mixed with the incoming salty crude oil from pipe line 5. The water and oil are then passed through orifice mixer l9 into pipe line section I as indicated by the arrows. The additional water, which is preferably fresh, may be introduced into pipe line section I by closing valve 32 and opening valve 33. This will direct the incoming fresh water from pipe lines l6 and I! through pipe line 34 into pipe line section I at connection 35. The salty oil and water will then pass through mixer l2 and heater l3 into the lower portion of tank 3 and will be dispersed by distributor 8. The cycle of operation will then repeat itself as previously described.

The desalted crude oil flows out continuously pipe line 21 has provision for maintaining a back pressure on the oil in the tank, as by weighted valve 31, constructed to maintain a suflicient back pressure to prevent evaporation of the water at the temperature maintained, such as lbs. per square inch where a temperature of from 300 to 500 F. is maintained.

In desalting crude petroleum by washing with water, it is customary to pass the oil directly onward into further processing, as passage through heat exchangers, pipe co'il heaters and rectifying equipment. The pressure drop incidental to the passage through the, processing equipment is carried on the oil from the time it leaves the charging pump. In the topping of most crudes. either by means of heat secured by exchange with hot vapors or residue from the heating coils, the refiner finds advantage by the imposi-- tion of pressure suflicient to prevent excessive evaporation up to the rectifying section of the um This incidental pressure is quite essential to take into consideration in this invention. As the temperatures available and customarily used at the salt settling sections of the refining units, range well above the atmospheric boiling point of water, it is obvious that this system must have means of retaining pressure as provided by valve 31.

The crude oil that is being desalted is usually relatively free of emulsions or emulsion elements and it is not usually necessary to treat it with chemicals in order to break down emulsions, but

. it is to be understood that the addition of chemicals at any point in the system to increase the effectiveness of the process may be practiced. A chemical dispenser is shown at 28 connected with the pipe section 6, and is used preferably and when necessary for introducing chemicals into the crude oil for preventing the formation of emulsions.

When chemicals are introduced into the system for the treatment of oils and oil emulsions, an accumulative benefit is accorded because of the recycling of the waterto which the chemicals have been added and due to the fact that a chemical that is dispersable in the water phase of an emulsion may be used, the chemical will be retained in the system; therefore, the treatmentis hastened and the amount of chemical needed to effect results is reduced.

While the invention has been described in connection with crude oil, it will be understood that the process may be applicable to fractions thereof, as where there is an initial distillation of light ends from the oil and the resulting residue subjected to the desalting process.

I claim:

1. A process for desalting crude oil or fractions thereof comprising contacting the oil with water in a continuous system having a settling chamber, in which the brine concentration is built up by the contacting and recontacting of incoming crude oil with water precipitated from the crude oil in the settling chamber, at a point outside the settling chamber, and maintaining the brine concentration by the introduction of water into the system and the release of excess brine from the system.

2. In a process of desalting crude oil or fractions thereof comprising using and reusing a body of water on a stream of oil passing continuously through the system while maintaining the body of water at a substantially constant condition of volume and degree of brine saturation in a settling chamber to permit of the highest degree of usefulness by contacting incoming crude oil or fractions thereof with precipitated water from the settling chamber at a point outside said chamber, passing the resulting mixture into said settling chamber, repeating said operations until the settled water has reached a predetermined degree of brineconcentration, then maintaining the concentration by introducing fresh or comparatively fresher water and maintaining the volume of the settled water.

3. A process of desalting crude oil or fractions thereof continuously by passing the oil through a system having a settling chamber, wherein the incoming crude is subjected to a flood contact of water from the settling chamber at a point outside said settling chamber and the water is settled out and maintained at a predetermined level by the wasting of excess water and the degree of brine saturation of the settled water is maintained at the desired degree by control of incoming water and the water is used to its useful limit.

4. In a process of desalting crude oil or fractions thereof, the system of simultaneously passing a stream of oil through the system, contacting the incoming oil with water from a settling chamber within the system at a point outside the settling chamber and the operation is repeated until the desired concentration of brine is secured, and this condition is maintained by the introduction of fresh or comparatively fresh water and the drawing out of the system of excess accumulations of brine.

5. A process of desalting crude oil or crude oil fractions by passing it in streams wherein it is first subjected to mixing with a predetermined amount of water fed in from sources outside the system, then again subjected to another mixing with water from a settling chamber within the system at a point beyond the two points of mixing, passing the mixture of oil and water to said chamber wherein the mixture is separated,

controlling the water level in said chamber by wasting excess water, controlling the degree of salt solution in said chamber by adding to or taking from the amount of water fed in the first mixing steps, and passing of! salt free oil from upper portion of settling chamber, all operations being continuous.

6. A process of intimately contacting predetermined ratios of fresh water from a source outside the system, and crude oil or fractions thereof, comprising passing them onward into intimate contact with any desired ratio of water and oil, said water being obtained in the second instance from the accumulated supply in the bottom of a settling chamber and into which the mixture is discharged and in which settling chamber the mixture is contained a period of time sufficient to permit settling and separation, the water being maintained in said chamber at the desired level by wasting excess and the brine saturation controlled by increasing or decreasing the volume of water fed into the system, and releasing desalted crude oil from the upper portion of the settling chamber, the oil being fed into and released from the system continuously.

7. A process of desalting crude oil or fractions thereof comprising" intimately contacting pre de termined ratios of oil and water in a recycling system in which the water is supplied from the base of a settling chamber of the system and mixing is accomplished by incoming oil outside the settling chamber, controlling the degree of brine saturation of the water by the addition of fresh water, and maintaining the level of the water in the chamber by wasting the excess water.

8. A process of desalting crude oil or fractions thereof in a system including a settling chamber having separated bodies of oil and brine, comprising mixing with the crude oil or fractions separated water from said chamber at a point outside the settling chamber, and passing said mixture into the chamber, adding fresh water to said mixture before discharging the same into the chamber, and controlling the supply of fresh water thereto directly in response to the salt concentration of the separated brine in the chamber as measured by its density.

9. A process of desalting crude oil or fractions thereof in a system including a settling chamber having separated bodies of oil and brine, comprising mixing with the crude oil or fractions separated water from said chamber at a point outside the settling chamber and passing said mixture into the chamber, adding fresh water to 7 said mixture before discharging the same into the chamber, and withdrawing the separated oil while maintaining a substantial back pressure greater than atmospheric on said chamber.

10. A process of desalting crude oil or fractions thereof continuously by passing the oil through a system having a settling chamber, wherein the incoming crude is subjected to a flood contact of water from the settling chamber before release of said oil below the water level in the settling chamber, which water is settled out and maintained at a predetermined level above the point of oil introduction by the wasting of excess water and the degree of brine concentration of the settled water is maintained at the desired degree by control of incoming water and the water is used to its useful limit.

11. A process of desalting crude oil or fractions thereof comprising contacting the oil with water in a continuous system having a settling chamber, in which the brine concentration is built up by the contacting and recontacting of incoming crude oil with water precipitated from the crude oil in the settling chamber, before release (if said incoming crude oil in the settling chamber, and maintaining the brine concentration by the introduction of water into the system and the release of excess brine from the system.

FRANK E. WELLMAN. 

